Field of the Invention
The present invention concerns wireless communications, and more specifically, to a method and apparatus of feeding back channel information in a wireless communication system.
Related Art
Next-generation multimedia wireless communication systems that have been recently actively being researched demand capability of processing and sending various types of information such as radio data and images as depart from voice-centered services that were presented earlier. 4rth generation wireless communication which is a successor of 3d generation wireless communication aims to support a high-speed data service up to a 1 Gbps (gigabits per second) downlink and a 500 Mbps (megabits per second) uplink. An object of the wireless communication system is to provide reliable communication regardless of the location and mobility of multiple users. However, wireless channels suffer from abnormal nature that arises from path loss, noise, multipath fading, inter-symbol interference, and Doppler effect due to the UE's mobility. Various techniques are on development so as to overcome the abnormal nature of wireless channel and raise reliability of wireless communication.
Meanwhile, as M2M (machine-to-machine) communication is introduced and various devices such as smartphones or tablet PCs are introduced and spread, the amount of data demanded over a cellular network is being quickly increased. To meet high data demand, various technologies are being introduced. Carrier aggregation (CA) and cognitive ratio (CR) technique for efficient use of more frequency bands are now in research. Further, multi-antenna technique and multi-base station cooperative technology for boosting up data capacity in a limited frequency band are being studied. Wireless communication systems are forecast to have higher node density. A wireless communication system having higher node density may enjoy enhanced performance thanks to inter-node cooperation. That is, a wireless communication system where each node is cooperative with others may present much better performance than a wireless communication system does in which each node operates as an independent base station (BS; base station), ABS (advanced BS), Node-B (NB), eNode-B (eNB), AP (access point).
In order to enhance the performance of a wireless communication system, a distributed multi-node system (DMNS, hereinafter, “multi-node system”) may apply where there are a plurality of nodes in a cell. The multi-node system may contain a distributed antenna system (DAS), a radio remote head (RRH) or the like. Further, standardization is now underway to apply various MIMO (multiple-input multiple-output) schemes and cooperative communication schemes, which have been already developed or are supposed to apply in the future, to the multi-node system.
Coordinated multipoint transmission and reception (CoMP) may apply to the multi-node system. Applying CoMP to a multi-cell multi-node system may lead to reduced inter-cell interference, and applying CoMP to a single cell multi-node system may result in reduced intra-cell inter-point interference.
As examples of CoMP, there are a JP (joint processing) scheme in which data on a UE is transmitted, shared by a plurality of nodes, and a CS (coordinated scheduling/beamforming) scheme in which data on a UE is transmitted by a single node that cooperates with other nodes through the other nodes' scheduling or a method of forming a transmission beam for reducing interference.
There is a need for a method of a UE efficiently measuring, generating, and feeding back channel information in a multi-node system.